Iron-chrome aluminium-alloy

ABSTRACT

The invention relates to an iron-chrome-aluminium-alloy with a high service life, comprising (in mass %)&gt;2-3.6% aluminium and &gt;10-20% chromium, and other added materials, namely, 0.1-1% Si, max. 0.5% Mn, 0.01-0.2% yttrium and/or 0.01-0.2% Hf and/or 0.01-0.3% Zr, max. 0.01% Mg, max. 0.01% Ca, max. 0.08% carbon, max. 0.04% nitrogen, max. 0.04% phosphorus, max. 0.01% sulphur, max. 0.05% copper and respectively max. 0.1% molybdenum and/or tungsten and the usual manufacture-related impurities, the remainder being iron.

[0001] Such alloys are used, inter alia, for the manufacture of electricheating elements and catalyst carriers. These materials form animpenetrable, adhesive aluminium oxide layer, which protects themagainst destruction. This protection is improved by additions of socalled reactive elements, such as for example Ca, Ce, La, Y, Zr, Hf, Ti,Nb, which improve the adhesiveness and/or reduce the layer growth, as itis described in the “Handbuch der Hochtemperatur-Werkstofflechnik”, RalfBurgel, Vieweg Verlag, Braunschweig 1998, form page 274 on.

[0002] The aluminium oxide layer protects the metallic material againstquick oxidation. Simultaneously, this layer grows but very slowly.During this growth, the aluminium content of the material is consumed.If there is no more aluminium, other oxides will grow (chromium and ironoxides). The metal content of the material is consumed very quickly andthen the material fails. The period until failing is called servicelife. Thus, an increase of the aluminium content increases the servicelife.

[0003] DE-A 19928842 describes an alloy comprising (in % by mass) 16 to22% Cr, 6 to 10% Al and additions of 0.02 to 1.0% Si, max. 0.5% Mn, 0.02to 0.1% Hf, 0.02 to 0.1% Y, 0.001 to 0.01% Mg, max. 0.02% Ti, max. 0.03%Zr, max. 0.02% Se, max. 0.1% Sr, max. 0.1%-max. 0.5% Cu, max. 0.1% V,max. 0.1% Ta, max. 0.1% Nb, max. 0.03% C, max. 0.01% N, max. 0.01% B,the rest being iron as well as manufacture related impurities for theuse as carrier foil for exhaust gas catalysts, as heat conductors, ascomponents in the construction of industrial furnaces and in gasburners.

[0004] EP-B 0387670 describes an alloy comprising (in % by mass) 20 to25% Cr, 5 to 8% Al and additions of 0.03 to 0.08% yttrium, 0.004 to0.008% nitrogen, 0.020 to 0.040% carbon, as well as approximately thesame proportions of 0.035 to 0.07% Ti and 0.035 to 0.07% zirconium, andmax. 0.01% phosphorus, max. 0.01% magnesium, max. 0.5% manganese, max.0.005% sulphur, the rest being reacted iron, the sum of the Ti and Zrcontents in % being 1.75 to 3.5 times higher than the C and N contentsin % by mass, as well as manufacture related impurities. Ti and Zr canbe completely or partially replaced by hafnium and/or tantalum orvanadium.

[0005] EP-B 0290719 describes an alloy comprising (in % by mass) 12 to30% Cr, 3.5 to 8% Al, 0.008 to 0.10% carbon, max. 0.8% silicium, 0.10 to0.1% manganese, max. 0.035% phosphorus, max. 0.020% sulphur, 0.1 to 1.0%molybdenum, max. 1% nickel, and the additions of 0.010 to 1.0%zirconium, 0.003 to 0.3% titanium and 0.003 to 0.3% nitrogen, 0.005 to0.05% calcium plus magnesium, as well as 0.003 to 0.80% rare earths,0.5% niobium, the rest being iron with usual companion elements, whichis for example used as wire of heating elements for electrically heatedfurnaces and as material for thermally stressed parts and as foil forthe manufacture of catalyst carriers.

[0006] U.S. Pat. No. 4,277,374 describes an alloy comprising (in % bymass) up to 26% chromium, 1 to 8% aluminium, 0.02 to 2% hafnium, up to0.3% yttrium, up to 0.1% carbon, up to 2% silicium, the rest being iron,with a preferred range of 12 to 22% chromium and 3 to 6% aluminium,which is used as foil for the manufacture of catalyst carriers.

[0007] The above documents are based upon traditional manufacturingmethods, such as the conventional casting of the alloy and thesubsequent hot and cold forming. Since these methods have high failurequota, inter alia due to embrittlements during hot rolling, alternativeshave been developed in the last years, in which a chromium steel, whichcontains reactive elements, is coated with aluminium or aluminiumalloys. Such composite materials are then rolled to their finalthickness and subsequently homogenized, wherein the setting of suitableannealing parameters leads to a homogenous material.

[0008] Such methods are for example described in the documents EP-B0640390, EP-B 0204423 and WO 99/18251, and they are extremely suitableto reduce the problems of processing for applications, where a highaluminium content is technically required and the material is used inform of foil or band.

[0009] Another possibility to reduce the failures and costs caused bythe embrittlements has been found in the use of iron-chromium-aluminiumalloys for household appliances, such as e.g. toaster, hair dryer andthe like, which are normally used at lower temperatures beneath 800° C.and manufactured under strict economic conditions. Since the material isusually used in form of wire here, the described solutions by coatingare not possible. Because of the low temperature stresses, alloyscomprising (in % by mass) a reduced aluminium content of beneath 5% areused here, such as for example an alloy comprising approximately 14.5%Cr, approx. 4.5% Al, additions of reactive elements, the rest beingiron, as it is produced and described in the DIN norm 17470 in table 3with 14% chromium and 4% aluminium, the rest being iron (Cr Al 14 4), asit is known from “Drähte von Krupp VDM für die Elektroindustrie”,publication N563, edition November 1998 on page 24, material Aluchrom Wcomprising 14 to 16% chromium, 3.5 to 5.0% aluminium, max. 0.08% carbon,max. 0.6% manganese, max. 0.5% silicium, max. 0.3% zirconium, othermanufacture related impurities, the rest being iron. In the following,this alloy serves as comparative alloy and is briefly called Cr Al 14 4.

[0010] Due to the aluminium content, which has been reduced toapproximately 4 to 4.5% by mass, the iron-chromium-aluminium alloy Cr Al14 4 can be manufactured more easily than the above described alloyscomprising more than 5% by mass aluminium. But it still showsembrittlements, which lead to a higher production effort during hotforming.

[0011] It has been the state of the art, that Fe Cr Al alloys comprisingapproximately 14 to 15% by mass chromium require a minimum content ofapproximately 4% by mass Al in order to build up a protective aluminiumoxide layer, as it is shown for example in “Handbuch derHochtemperatur-Werkstofflechnik”, Ralf Burgel, Vieweg Verlag,Braunschweig 1998, on page 272 in image 5.13.

[0012] GB-A 476,115 discloses an iron alloy, which can in particular beused as electric resistance and comprises the following elements:6.1-30% Cr, 3-12% Al, 0.07-0.2% C, <4% Ti, the rest being Fe as well asmanufacture related impurities. Herein, the Ti content is related to theC content, such that it shall not be less than 3 times the C content.Preferred ranges of Cr are >8%, of Al>5%, of C>0.085%.

[0013] DE-A 196 52 399 describes a method for manufacturing amulti-layer metal compound foil as well as the use thereof. The metalcompound foil includes a carrier layer made of ferritic steel band,which is provided on both sides with an external layer of aluminium oraluminium alloy. The carrier layer is formed by an alloy comprising (in% by mass) 16-25% Cr, rare earths, Y or Zr contents comprised between0.01 and 0.1%, the rest being Fe. Furthermore, Al contents comprisedbetween 2 and 6% can be added by alloying. Preferred Cr contents areabove 20%.

[0014] Finally, EP-A 0 402 640 discloses a rust-free steel foil ascarrier element for catalysts as well as the manufacture thereof. Thefoil is formed by an alloy having the following composition (in % bymass): 1.0-20% Al, 5-30% Cr, up to 2% Mn, up to 3% Si, up to 1% C, therest being Fe as well as manufacture related impurities. Preferredcontents of Al are comprised between 5,5 and 20%. Furthermore, amountsof up to 0.3% of Y, Sc or rare earths can be added by alloying, whereincontents of up to 2% of at least one of the elements Ti, Nb, Zr, Hf, V,Ta, Mo, W can also be provided. Herein, contents of <4% Al require Crcontents of >25%.

[0015] It is the object of the invention to provide a low cost ironchromium aluminium alloy, which has a similar or better service lifethan Cr Al 14 4, but has a still lower brittleness and thus improvedformability, and simultaneously has the same technical functionality asCr Al 14 4.

[0016] This aim is achieved by an iron chromium aluminium alloy having along service life comprising (in % by mass)>2 to 3.6% by mass aluminiumand >10 to 20% chromium as well as additions of 0.1 to 1% Si, max. 0.5%Mn, 0.01 to 0.2% yttrium and/or 0.01 to 0.2% Hf and/or 0.01 to 0.3% Zr,max. 0.01% Mg, max. 0.01 Ca, max. 0.08% carbon, max. 0.04% nitrogen,max. 0.04% phosphorus, max. 0.01% sulphur, max. 0.05% copper andrespectively max. 0.1% molybdenum and/or tungsten as well as manufacturerelated impurities, the rest being iron.

[0017] Advantageous embodiments of the alloy according to the inventionare disclosed in the sub-claims.

[0018] Preferably, the Al content can be set within the limits of2.5-3.55% and the Cr content within the limits of 13-17%.

[0019] A reduction of the brittleness can be achieved the mostefficiently by reducing the aluminium content. But this has the drawbackthat the specific electric resistance also decreases and the servicelife becomes shorter.

[0020] The brittleness is also increased by chromium, silicium, carbonand nitrogen, so that these elements should also be kept as low aspossible.

[0021] The same technical functionality is achieved for a heatconductor, which serves for the electrical production of heat, when thesurface performance, the performance at the heating element, the totalresistance of the heating element and the service life of the heatingelement remain constant in spite of any modification of the material.

[0022] If the specific electric resistance is reduced while keeping thesurface performance, the performance and the resistance constant, thediameter of the wire has to be reduced and the wire length has to beincreased by the same percentage by which the diameter has been reduced,in order to be able to meet the above requirements. Therewith, thevolume is reduced by this percentage. This means, material is saved whenthe specific electric resistance is reduced. This is also disclosed inH. Pfeifer, H. Thomas “Zuzunderfeste Legierungen”, Springer Verlag,Berlin 1963, on page 387.

[0023] The following calculation illustrates this fact:

[0024] The diameter, length and weight modification caused by thereplacement of material A with B is calculated for wires, wherein thesurface performance, performance and resistance are kept constant.

[0025] The following formulas are fulfilled under the above conditions:

Diameter D _(B) /D _(A={cube root}{square root over (ρB/ρA)})

Length L _(B) /L _(A)={cube root}{square root over (ρ_(A)/ρ_(B))}

Weight M _(B) /M _(A)={cube root}{square root over(ρ_(B)/ρ_(A)·γ_(B)/γ_(A))}

[0026] When the alloy according to the invention is used as wire, forexample for a heating element, with a diameter D_(B), which has beenchanged according to

D _(B) /D _(A)={cube root}{square root over (ρ_(B)/ρ_(A))}

[0027] and a length L_(B), which has been changed according to

L _(B) /L _(A)={cube root}{square root over (ρ_(A)/ρ_(B))}

[0028] a material amount of an alloy B, which is smaller by

M _(B) /M _(A)={cube root}{square root over (ρ_(B)/ρ_(A))}·γ_(B/γ) _(A)

[0029] is required for the wire having the specific electric resistanceρ_(B), which has the same functionality in comparison to the wire madeof an alloy A and having the specific electric resistance ρ_(A) thediameter D_(A) and the length L_(A), if ρ_(B) is smaller than ρ_(B) andapproximately γ_(A)≈γ_(B).

[0030] Example: material A: ρ_(A)=1.25 Ωmm²/m

[0031] material B: ρ_(B)=1.05 Ωmm²/m

[0032] D_(B)/D_(A)=0.94; i.e. reduction of the diameter by 6% by mass

[0033] L_(B)/L_(A)=1.06; i.e. increase of the length by 6% by mass

[0034] M_(B)/M_(A)=0.94; i.e. reduction of the weight by 6% by mass %

[0035] wherein the densities are assumed to be γ_(A)≅γ_(B) in thisexemplary theory. In a concrete case, the validity of this assumptionhas to be verified.

[0036] But this idea has not been realised so far, since the reductionof the diameter leads to a reduction of the service life.

[0037] In the following the service life reduction caused by thereduction of the wire diameter is estimated:

[0038] According to I. Gurrappa, S. Weinbruch, D. Naumenko, W. J.Quadakkers, Materials and Corrosions 51 (2000), pages 224 through 235,the service life t of a wire can be calculated with:$t = {{\left\lbrack {4.4 \times 10^{- 3} \times \left( {C_{0} - C_{K}} \right) \times \frac{\gamma \cdot f}{k}} \right\rbrack^{1/n}\quad {with}\quad f} = \frac{D}{2}}$

[0039] for wire having the diameter D

[0040] γ=density of the alloy

[0041] C₀=aluminium concentration of the alloy before start of theoxidation or use of a heating spiral

[0042] C_(K)=critical aluminium concentration, at which the break awayoxidation, i.e. the formation of other oxides than the aluminium oxides,starts. This indicates the end of the operativeness of a heat conductorand leads to the rapid fusion of the heat conductor and can thus beregarded as the end of service life.

[0043] k=oxidation constant

[0044] n=oxidation rate exponent having a value of approximately 0.5

[0045] The oxidation constant k is a measuring tool for the quality ofthe oxide layer. For an oxide layer, which provides a very goodprotection, k is smaller than for an oxide layer of lower quality. Thesmaller k is the longer is the service life.

[0046] If, according to the above theory, for one alloy the wirediameter is reduced by the factor 0.94, the service life is reduced asfollows, since the oxidation constant k, the density y, C₀ and C_(K)remain the same:$\frac{t_{2}}{t_{1}} = {\left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack^{1/n} = {\left\lbrack {0,95} \right\rbrack^{2} = {0,88}}}$

[0047] with t₁=service life with the greater wire diameter D₁

[0048] and t₂=service life with the smaller wire diameter D₂.

[0049] This means that an alloy with the same functionality would haveto have a 12% higher service life, in order to compensate the drawbackof the smaller wire diameter. Even higher service lives offer theadditional advantage of a longer service life, i.e. an improvedfunctionality.

[0050] Surprisingly it has been found that alloys comprising (in % bymass)>2 to 3.6% aluminium and >10 to 20% chromium, and additions of 0.1to 1% Si, max. 0.5% Mn, 0.01 to 0.2% yttrium, and/or 0.01 to 0.2% Hfand/or 0.01 to 0.3% Zr, max. 0.01% Mg, max. 0.01% Ca, max. 0.08% carbon,rest iron and the usual manufacture related impurities have a muchbetter service life than the alloy, which has been used so far and whichcomprises approximately 14.5% Cr, approximately 4.5% Al and additions ofmax. 0.3% zirconium, max. 0.08% carbon, max. 0.6% manganese, max. 0.5%silicium, rest iron and other manufacture related impurities.

[0051] The subject of the invention can be used, besides for heatconductors for heating elements, e.g. a household appliance, or asmaterial in the construction of furnaces, also as foil, for example ascarrier foil for catalysts.

[0052] The advantages of the invention will be explained in detail inthe following examples:

EXAMPLES

[0053] In table 1 the different iron chromium aluminium alloys arelisted, wherein the table contains both big scale batches and batchesproduced in the laboratory.

[0054] For heating elements (heat conductors) in form of wire,accelerated service life tests are possible for the comparison ofmaterials with each other, for example under the following conditions:

[0055] The test is carried out with wires having a diameter of 0.40 mm,from which wire spirals having 12 turns, a spiral diameter of 4 mm and aspiral length of 50 mm are manufactured. The wire spirals are clampedbetween 2 current supplies and heated up to 1200° C. by applying avoltage. They are heated for respectively 2 minutes, then the currentsupply is interrupted for 15 seconds. At the end of the service life,the wire fails in that the remaining cross section melts. The totalperiod of time, within which the wire was heated, without theinterruptions, is indicated as service life and called burning time inthe following.

[0056] The big scale batch T1 and the lab scale batches T2 and T3represent the state of the art for Cr Al 14 4, comprising (in % by mass)approximately 14.5% chromium, 4.5% aluminium, approx. 0.3% manganese,approx. 0.2% silicium, and 0.17% to 0.18% zirconium as reactive element.The lab scale batch T3 has a service life of 49 hours, the lab scalebatch T2 has a service life of 63 hours and the big scale batch T1 has aservice life of 77 hours. The batches H1 through H6 are batches with analuminium content of more than 5% by mass and different additions ofsilicium, manganese, zirconium, titanium, hafnium and yttrium and otheradditions, such as for example calcium, magnesium, carbon and nitrogen.As it was to expect, they all show a clearly longer service life incomparison to the batches T1 through T3 because of the higher aluminiumcontent. Differences of the service life of H1 through H6 are inparticular caused by the different contents of aluminium, silicium,zirconium, titanium, hafnium and yttrium.

[0057] For the lab scale batch K1, the aluminium content has beenreduced from 4.5 to 3.55% by mass in comparison to the lab scale batchT2 according to the state of the art. The service life was thus reduced,as expected, from 63 hours to 34 hours.

[0058] This is not the case for the batches L2, L3, M1, M2 and M4according to the invention and marked with “E”. In comparison to the labscale batches T3 and T2 according to the state of the art, they have aservice life, which is increased by the factor 1.5 to 2, although theycomprise clearly lower aluminium contents of 2.5 to 3.6% by mass. Theircommon characteristic is that they contain, besides zirconium, alsoyttrium and/or hafnium. Therein, batch L2 comprising an aluminiumcontent (in % by mass) of 2.55% and a zirconium content of 0.05% and ahafnium content of 0.04% and an yttrium content of 0.02% reaches aservice life of 109 hours. Batch L3 comprising an aluminium content of3.55% and a zirconium content of 0.053% and a hafnium content of 0.042%and an yttrium content of 0.02 reaches a service life of 90 hours. BatchM1 comprising an aluminium content of 2.78% and a zirconium content of0.05% and a hafnium content of 0.03% and an yttrium content of 0.02%reaches a service life of 92 hours. Batch M2 comprising an aluminiumcontent of 2.71% and a zirconium content of 0.05% and a hafnium contentof 0.03% and an yttrium content of 0.04% reaches a service life of 126hours. Batch M4 comprising an aluminium content of 2.8% and a zirconiumcontent of 0.03% and a hafnium content of 0.03% and an yttrium contentof 0.03% reaches a service life of 85 hours.

[0059] These examples show that, in spite of low aluminium contents,very small additions of zirconium, hafnium and yttrium to the ironchromium aluminium alloy make it possible to obtain very high servicelives, which correspond to those of iron chromium aluminium alloyscomprising more than 5% aluminium.

[0060] Summing up, it may be said that the alloy according to theinvention must contain additions of 0.01 to 0.2% yttrium and/or 0.01 to0.2% Hf and/or 0.01 to 0.3% Zr.

[0061] Batch L1 shows that in spite of an addition of zirconium, hafniumand yttrium, only a service life of 9.3 hours will be obtained with analuminium content of 1.55%. Batch M3 comprising an aluminium content ofonly 2.24% also has a service life of only 72 hours in spite of anaddition of zirconium, hafnium and yttrium, which service lifecorresponds to those of the batches according to the state of the art.The alloy according to the invention should thus have an aluminiumcontent of more than 2%.

[0062] Chromium contents comprised between 14 and 17% have no decisiveinfluence on the service life, as it is shown by the comparison of thezirconium, hafnium and yttrium bearing batches Ml comprising 14.85%chromium and 2.78% aluminium and batch L2 comprising 16.86% chromium and2.55% aluminium. However, a certain chromium content is necessary, sincechromium stimulates the formation of the highly stable and protectiveα-Al₂O₃ layer. According to H. M. Herbelin, M. Mantel, Colloque C7,Supplement au Journal de Physique III, Vol. 5, November 1995, pagesC7-365 through 374, this is still the case for a chromium content of13%, but a chromium content of 6% is no more sufficient.

[0063] According to J. Klower, Materials and Corrosion 51 (2000), pages373 through 385, additions of approx. 0.3% by mass silicium and moreincrease the service life by improving the adhesiveness of the coverlayer. Therefore, a content of at least 0.1% silicium is required.

[0064] In table 1 the notched bar impact work at room temperature, 50°C., 100° C. and 150° C. is listed for DMV norm samples (cf. W. Domke,Werkstoffkunde und Werkstoffprüfung, Verlag W. Geradet, Essen 1981, frompage 336 on). The notched bar impact work of a ferritic steel is low,when a brittle fracture occurs at low temperatures (low position) and ishigh for the ductile, easily formable behaviour at higher temperatures(high position) with a steep increase within a few degrees from the lowposition to the high position. Therein, the notched bar impact work canhighly scatter in this range. The temperature, at which the transitionfrom the high position into the low position takes place, is callednotch transition temperature. A material is for example the morebrittle, the greater the grain size is, or for the iron chromiumaluminium materials, the higher the content of alloying elements, suchas aluminium, chromium, silicium, nitrogen, carbon, phosphorus andsulphur, is. Due to their preparation as lab scale batch, all notchedbar impact samples in table 1 have a very big grain size of about 200 to400 μm, which is very unfavourable. Therefore, all samples are in thelow position at room temperature, wherein the samples comprising thelowest aluminium content, the lowest chromium content and the lowestcarbon content, have the highest notched bar impact work, as the batchesM1, M2, M3, M4 and L1 show. Batch M4 has a slightly worse and lowernotched bar impact work than batch M2 having a similar aluminium andchromium content, since the first one has a higher carbon content. BatchL2 has a slightly lower notched bar impact work than batch M2, since ithas a higher chromium content. Nitrogen, phosphorus and sulphur have asimilar effect as carbon, so that their contents should advantageouslybe kept low. It has been found that the aluminium content may not exceed3.6% in order to keep the embrittling effect of the aluminium as smallas possible.

[0065] The same situation exists for the notched bar impact worksmeasured at 50° C. and 100° C., only that the improvement of the notchedbar impact works is still more clear for the low aluminium contents andthe reduction of the notched bar impact work due to an increased carboncontent of M4 in comparison to M1 and M2 can be seen still more clearly.One can also see here, that batch M1, which differs from batch M2 by ahigher silicium content, has a slightly lower notched bar impact work.At 150° C. all notched bar impact works are in the ductile highposition, wherein the batches M2, M3 and M4 having an aluminium contentof 2.2 to 2.8% present the highest notched bar impact works.

[0066] Summing up, it may be said that the brittle behaviour of the ironchromium aluminium alloys is clearly reduced by decreasing the aluminiumcontent to beneath 3.6%. This is additionally supported by low contentsof silicium, carbon, nitrogen, phosphorus and sulphur. The carboncontent is therefore limited to max. 0.08%, the nitrogen content to max.0.04%, the phosphorus content to max. 0.04% and the sulphur content tomax. 0.01% by mass. Phosphorus and sulphur additionally have a negativeeffect on the service life, so that also from this point of view, lowcontents of these elements are advantageous.

[0067] For the reason of the embrittling effect, the chromium contentshould also be provided as low as possible. Because of the requirementsconcerning the service life, the silicium and chromium contents cannotbe reduced to almost zero, but have to be at least 0.1% silicium and 10%chromium. But no more than 20% chromium and 1% silicium should be added,in order to achieve a brittleness, which is as low as possible.

[0068] If an alloy Cr Al 14 4, as it is represented in table 1 forexample by the batches T1, T2 and T3, is replaced with an alloyaccording to the invention, such as for example with the batches M2 orM4, the specific electric resistance is reduced from 1.21 Ωmm²/m (alloyA) to 1.04 Ωmm²/m (alloy B). According to the above statements, the samefunctionality will be assured, if surface performance, performance andresistance of the heating spiral are kept constant.

[0069] Therein, the following results for

the diameter relation: D _(B) /D _(A)={cube root}{square root over(ρ_(B)/ρ_(A))}=0.95

and for the length relation: L _(B) /L _(A)={cube root}{square root over(ρ_(A)/ρ_(B))}=1.05

the weight relation M _(B) /M _(A)={cube root}{square root over(ρ_(B)/ρ_(A))}·γ_(B)/γ_(A)=0.95 with

approximately γA≅γ_(B)

[0070] The density of alloy A is γ_(A)=7.12 g/cm², the density of alloyB is γ_(B)=7.30 g/cm². Considering the modification of the density, theweight relation results only slightly higher in:

M _(B) /M _(A)={cube root}{square root over(ρ_(B)/ρ_(A))}·γ_(B)γ_(A)=0.95

[0071] This means that the approximate estimation of γ_(A)=γ_(B) wasadmissible in this case.

[0072] The service life estimation according to 1. Gurrappa, S.Weinbruch, D. Naumenko, W. J. Quadakkers, Materials and Corrosions 51(2000), pages 224 through 235 by reduction of the wire diameter of thealloy B according to the invention results in:$\frac{t_{2}}{t_{1}} = {\left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack^{1/n} = {\left\lbrack {0,95} \right\rbrack^{2} = {0,90}}}$

[0073] This means that the alloy according to the invention must have aservice life, which is at least 10% longer, in order to compensate thedrawback of the smaller wire diameter. But since the batches accordingto the invention all have an at least 50% higher service life, the useof the alloy according to the invention offers the additional advantageof a longer service life.

[0074] Manganese is limited to 0.5% by mass, since this element reducesthe oxidation stability. The same is valid for copper. TABLE 1 Examplesof iron chromium aluminium alloys (service life corresponds to burningtime) ρ in batch Mn Cr Si Al Mg Ca Zr Ti Hf Y N C P S Ωmm²/m¹) Big scalebatches T1 0.31 14.5  0.2  4.45 0.01 0.17 0.01 — — 0.005 0.02  0.0130.002 1.21 H1 0.19 20.5  0.32 5.05 0.01 0.003 0.17 0.01 — — 0.007 0.0210.010 0.002 1.30 H2 0.21 20.85 0.14 5.2  0.01 0.001 0.05 0.06 — 0.060.008 0.032 0.013 0.002 1.33 H3 0.22 20.75 0.14 5.1  0.006 0.002 0.050.06 — 0.07 0.007 0.036 0.014 0.002 1.32 H4 0.19 20.0  0.30 5.62 0.0090.004 0.04 0.04  0.06 0.003 0.025 0.013 0.002 1.38 H5 0.10 21.01 0.245.65 0.006 0.0006 0.10 0.009 — — 0.014 H6 0.24 22.21 0.03 5.83 0.0020.003 0.228 0.105 — — 0.026 0.016 0.001 1.39 Lab scale batches T2 0.3314.4  0.22 4.5  0.0033 3 ppm 0.18 <0.01 — — 0.006 0.026 0.004 0.004 1.21K1 0.33 14.4  0.44 3.55 0.0033 3 ppm 0.18 <0.01 — — 0.004 0.025 0.0040.004 1.15 L1 0.26 16.90 0.37 1.55 0.002 0.049 <0.01 0.039 0.02 0.0020.003 0.002 0.002 0.91 E L2 0.26 16.86 0.38 2.55 0.002 0.050 <0.01 0.0400.03 0.003 0.002 0.002 0.002 1.06 E L3 0.27 16.61 0.38 3.55 0.002 0.053<0.01 0.042 0.04 0.003 0.018 0.003 0.003 1.17 T3 0.30 14.70 0.20 4.490.0034 5 ppm 0.18 <0.01 — <0.01   0.002 0.002 0.003 0.004 1.21 E M1 0.3614.85 0.50 2.78 0.0033 6 ppm 0.05 <0.01 0.03  0.02 0.004 0.002 0.0030.002 1.07 E M2 0.35 14.80 0.28 2.71 0.0034 5 ppm 0.05 <0.01 0.03  0.040.004 0.002 0.003 0.004 1.04 M3 0.36 14.80 0.28 2.24 0.0032 4 ppm 0.05<0.01 0.03  0.02 0.002 0.002 0.003 0.002 0.92 E M4 0.30 14.65 0.3  2.8 <0.001 <0.001 0.03 <0.01 0.03  0.03 0.0015 0.018 0.002 0.002 1.03Notched bar impact work in J Service life at 13 mm WB²) 1200° C. RT 50°C. 100° C. 150° C. hours 77 119 137 99 117 111 111 7 63 9 34 11 9.3 E 8109 E 8 90 8 8.1 35 120 49 E 10 20 92 E 10 24 143 272 126 19 102 >300285 72 E 9 13 85 179 85

1. An iron chromium aluminium alloy with long service life comprising(in % by mass)>2 to 3.6% aluminium and >10 to 20% chromium as well asadditions of 0.1 to 1% Si, max. 0.5% Mn, 0.01 to 0.2% yttrium and/or0.01 to 0.2% Hf and/or 0.01 to 0.3% Zr, max. 0.01% Mg, max. 0.01% Ca,max. 0.08% carbon, max. 0.04% nitrogen, max. 0.04% phosphorus, max.0.01% sulphur, max. 0.05% copper and respectively max. 0.1% molybdenumand/or tungsten, as well as manufacture related impurities, the restbeing iron.
 2. An iron chromium aluminium alloy according to claim 1comprising (in % by mass) 2.5 to 3.55% aluminium, 13 to 17% by masschromium and additions of 0.1 to 0.5% Si, max. 0.5% Mn, 0.01 to 0.1%yttrium and/or 0.01 to 0.1% Hf and/or 0.01 to 0.2% Zr, max. 0.01% Mg,max. 0.01% Ca, max. 0.08% carbon, max. 0.04% nitrogen, max. 0.04%phosphorus, max. 0.01% sulphur, max. 0.05% copper and respectively max.0.1% molybdenum and/or tungsten, as well as manufacture relatedimpurities, the rest being iron.
 3. An iron chromium aluminium alloyaccording to claim 1 or 2 comprising (in % by mass) 2.5 to 3.0%aluminium and 14 to 17% chromium and additions of 0.1 to 0.5% Si, max.0.5% Mn, 0.01 to 0.08% yttrium and/or 0.01 to 0.08% Hf and/or 0.01 to0.08% Zr, max. 0.01% Mg, max. 0.01% Ca, max. 0.08% carbon, max. 0.04%nitrogen, max. 0.04% phosphorus, max. 0.01% sulphur, max. 0.05% copperand respectively max. 0.1% molybdenum and/or tungsten, as well asmanufacture related impurities, the rest being iron.
 4. An iron chromiumaluminium alloy according to one of the claims 1 through 3, in which oneor more of the elements yttrium, hafnium or zirconium can be replacedcompletely or partly by (in % by mass) 0.01 to 0.1% of one or more ofthe elements scandium and/or titanium and/or vanadium and/or niobiumand/or tantalum and/or rare earths, such as in particular lanthanumand/or cerium.
 5. An iron chromium aluminium alloy according to one ofthe claims 1 through 4, characterized in that the carbon content islimited to 0.02%, the nitrogen content is limited to 0.01%, thephosphorus content is limited to 0.01% and the sulphur content islimited to 0.005%.
 6. An iron chromium aluminium alloy according to oneof the claims 1 through 5, wherein the following conditions with respectto the diameter, length and weight modification are given, if the alloyis used as wire and if the surface performance, the performance as wellas the resistance are kept constant and if a material A is replaced witha material B: diameter D _(B) /D _(A)={cube root}{square root over(ρ_(B)/ρ_(A))}length L _(A) /L _(B)={cube root}{square root over(ρ_(B)/ρ_(A))}weight M _(B) /M _(A)={cube root}{square root over(ρ_(B)/ρ_(A))}·γ_(B) /γ _(A) wherein D is the diameter p is the specificelectric resistance L is the length M is the weight γ is the density ofthe respective wire.
 7. Use of an iron chromium aluminium alloyaccording to one of the claims 1 through 6 as heat conductor in aheating element.
 8. Use of an iron chromium aluminium alloy according toone of the claims 1 through 6 as alloy, especially in form of a heatingelement, for the use in a household appliance.
 9. Use of an ironchromium aluminium alloy according to one of the claims 1 through 6 asalloy, especially in form of a heating element or as material for theuse in the construction of furnaces.
 10. Use of an iron chromiumaluminium alloy according to one of the claims 1 through 6 as alloy,especially in form of a foil, for the use as carrier foil of catalysts.11. Use of an iron chromium aluminium alloy according to one of theclaims 1 through 6 as alloy, especially in form of wire or band, for theuse as braking and starting resistance.